In the field of geochemical research and petroleum exploration, an area of growing interest is analysis of geological samples to determine the remaining petroleum generating potential of the rock sample. Work in this field has been directed to methods for removing hydrocarbons from geological samples and analyzing the hydrocarbons, to apparatuses for laboratory and field analysis for geological samples, and to the development of theoretical and practical models for predicting petroleum exploration related characteristics for the raw data obtained.
Direct assessment of actual petroleum potential for any kerogen (insoluble organic portion of a sedimentary rock) system is vital for Sedimentary Basin Modelling in oil exploration. Pyrolysis-gas chromatography (pyrolysis-GC) techniques have proven successful in providing vital information in determining kerogen characteristics, oil-source rocks correlations, petroleum generation kinetics, gas-oil ratios (GOR) and precursor product relationships with a view, among others applications, to determining catagenic petroleum yield and composition. However, conventional pyrolysis-GC fingerprinting is often a subjective process and therefore to be useful, kerogens should be classified at the same molecular level, as is possible with crude oils; thus full quantitation of all pyrolysis products is desirable.
In performing analyses of the type described above, it is desirable to be able to make accurate, reproducible determinations of quantity of volatile hydrocarbons present in the geological sample.
Hydrocarbons may be quantitated using a methylstyrene internal standard generated during the pyrolysis process from polymethylstyrene admixed with kerogen as discussed in Larter et al. Nature (London) 318, 277,278 (1985) Poly-para-t-butyl-styrene has been similarly used. See Oygrad et al., Org. Geochem., 13, 1153 (1988). In addition, products are also quantified with reference to phenylhexane, both external and internal, by peak area integration. See Horsefield et al., Geol. Rund., 78, 361 (1989).
Quantification is also done by gas chromatography using the branched and cyclic hydrocarbon fraction of a crude oil as an external standard. See Vandenbroucke et al., Org. Geochem., 7,961 (1993). However, the above internal and external standards are generally thermally unstable and chemically reactive with the potential of forming reaction products which could interfere with peaks of interest during sealed tube pyrolysis.
Therefore it is an object of the present invention to provide an on-line quantitative pyrolysis-GC method whereby the internal standard is thermally stable during oil and gas generation temperatures. It is a further object of the present invention to provide an on-line quantitative pyrolysis-GC method whereby the internal standard is chemically unreactive during oil and gas generation temperatures.